Harry can prepare a king's shed -- look! (10)
I believe the answer is:
appearance
'look' is the definition.
(I have seen 'The look' mean 'appearance' so perhaps 'look' could also mean 'appearance')
'harry can prepare a king's shed' is the wordplay.
'harry' indicates an anagram (harry can mean to attack or spoil).
'king' becomes 'R' (abbreviation of Latin rex).
'shed' indicates named letters should be taken away ('shed' as in 'cut away').
'can'+'prepare'+'a'='canpreparea'
'canpreparea' with 'r' taken out is 'canpeparea'.
'canpeparea' anagrammed gives 'APPEARANCE'.
(Other definitions for appearance that I've seen before include "Advent" , "Someone present has put one in" , "Semblance" , "Outward look" , "show" .)